The present invention relates to a method by which, when producing semiconductor devices, the inside of a pneumatic device through which interhalogen compound gas such as ClF.sub.3 or the like passes, is opened to atmosphere while assuring the safety, and also relates to a variety of devices to which such a method can be applied.
In the field of producing semiconductor devices, attention is recently given to interhalogen compound gas such as ClF.sub.3 gas or the like serving as gas with which semiconductor wafers are etched, CVD is conducted or the inside of a chamber or the like is cleaned. However, the interhalogen compound gas has the following nature to which care must be used in handling the same.
For example, a ClF.sub.3 molecule which is an interhalogen compound, has a Cl--F binding energy as small as 258.6 KJ/mol and has the nature that Cl is separated from F to fluorinate other substance. With the use of such nature, ClF.sub.3 gas is proposed (i) as cleaning gas for regularly removing a layer such as a polysilicon layer, a silicon carbide layer or the like formed on the inner wall of a chamber or the like forming a reaction chamber in a CVD apparatus (U.S. Pat. No. 4,998,979) or (ii) as etching gas for etching a polysilicon layer, a silicon nitride layer or the like (Japanese Patent Laid-Open Publication 2-68948). In particular, the interhalogen compound gas such as ClF.sub.3 gas or the like has a strong reactivity that it reacts with silicon at room temperature even though it is not brought in a state of plasma. Accordingly, the interhalogen compound gas can fulfill excellent function in an etching process or the like. However, having such a strong reactivity means that the interhalogen compound gas is considerably toxic. For etching gas, there is determined a TLV value or gas concentration under which work for 8 hours or more is dangerous. Based on such a TLV value, there is judged the toxicity of etching gas. While the TLV value of prevailing etching gas such as chlorine, HF, HCl, HBr or the like, is 1 ppm, the TLV value of ClF.sub.3 gas is 0.1 ppm, which is equivalent to toxicity of 10 times or more of chlorine gas or the like.
It is therefore required to lower residual ClF.sub.3 gas in concentration to assure the safety of workers when replacing a part of a reaction chamber or a pneumatic device such as a pump or the like in which ClF.sub.3 gas is used, when replacing a ClF.sub.3 gas bomb or when replacing a medicine for a waste gas processing device. To lower the concentration of residual reactive gas, there has conventionally been made provision to generate plasma using safe gas such as SF.sub.6 or the like or to substitute the atmosphere with inert gas such as dry nitrogen or the like. The reason of why dry nitrogen having humidity not greater than 1% has been used, is because a reaction product, hydrochloric acid, of moisture with reactive gas, in particular chlorine-type gas, readily corrodes metal.
On the other hand, the following techniques are available as a method of cleaning, flushing, purging, or removing a halogen-element-containing gas which remains in a chamber or component into which the halogen-element-containing gas has been introduced.
For example, Japanese Patent Laid-Open Publication 4-323389 discloses a method of passing, through the chamber, inert gas or air containing moisture not less than a predetermined value, such that residual halogen gas is removed.
Japanese Patent Laid-Open Publication 5-243163 discloses a method by which inert gas or air heated to not less than 50.degree. C. is passed through a chamber into which halogen-element-containing gas has been introduced, such that residual halogen-element-containing gas is removed.
In each of the techniques in the publications above-mentioned, the residual halogen-element-containing gas is removed to prevent the chamber forming the reaction chamber from being corroded.
Out of examples of the halogen-element-containing gas, the interhalogen compound gas is very strong in reactivity. Accordingly, it is turned out that, when moisture-containing-air or moisture-containing-inert gas is introduced, according to any of the techniques of the publications above-mentioned, into the chamber in which the interhalogen compound gas remains, metal such as aluminium, SUS or the like forming the inner wall of the chamber is immediately corroded. When iron oxide or the like is produced, even in a small amount, due to the corrosion of metal, metallic ions produced as a result of decomposition of the iron oxide or the like in plasma at the time of a CVD processing or the like, mixingly enter a semiconductor material. This exerts serious adverse effect on the semiconductor device. Accordingly, each of the techniques discussed in the publications above-mentioned is effective for SF.sub.6 gas, NF.sub.3 gas, CF.sub.4 gas in preventing the corrosion of the chamber forming the reaction chamber, but results in acceleration of corrosion with respect to interhalogen compound gas such as ClF.sub.3 gas or the like.
Thus, to remove interhalogen compound gas remaining in the chamber or the like, there is only available a conventional method of utilizing the generation of SF.sub.6 plasma or of substituting the atmosphere in the chamber with inert gas such as nitrogen gas or the like.
However, the interhalogen compound gas such as ClF.sub.3 gas or the like has strong toxicity and high adsorptivity with respect to metal such as SUS, aluminium or the like. Accordingly, for example when it is intended to lower the concentration of interhalogen compound gas remaining in the vacuum system or the pump unit by utilizing the generation of SF.sub.6 plasma or by substituting the atmosphere with nitrogen gas, it takes much time to lower the concentration of ClF.sub.3 gas adsorbed to the inner wall of the chamber, to not greater than the TLV value. For example, as to substitution with nitrogen gas, even though the atmosphere was substituted with dry nitrogen for 24 hours, the concentration of the ClF.sub.3 gas in the pipes could not be lowered to not greater than 0.1 ppm.